Semiconductor device and manufacturing method thereof

A method comprising:

• depositing a Ge-containing semiconductive layer over a substrate;
• patterning the Ge-containing semiconductive layer to form a Ge-containing channel region over the substrate;
• depositing a Si-containing semiconductive layer over the substrate and covering the Ge-containing channel region;
• forming an oxidation layer over the Si-containing semiconductive layer;
• performing an annealing process to the oxidation layer;
• and
• depositing a gate dielectric layer to cover the Si-containing semiconductive layer after performing the annealing process;
• and
• depositing a gate electrode over the gate dielectric layer.

A device comprising:

• a Ge-containing channel structure;
• a gate structure over the Ge-containing channel structure, wherein the gate structure comprises:
• a gate dielectric layer covering the Ge-containing channel structure;
• and
• a gate electrode covering the Ge-containing channel structure;
• gate spacers on opposite sides of the gate structure;
• and
• a semiconductive layer between the gate dielectric and the Ge-containing channel layer, wherein a germanium atomic percentage of the semiconductive layer is lower than a germanium atomic percentage of the Ge-containing channel structure, and the semiconductive layer is in contact with the gate spacers.